CVE-2026-107579 Inefficient Algorithmic Complexity in hMailServer
Remote attackers can cause denial of service in hMailServer by sending crafted messages that trigger inefficient processing, requiring bounce or complaint features to be enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-107579?
CVE-2026-107579 is a high-severity denial of service vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Inefficient algorithmic complexity in the bounce and complaint processing of Progressive Robot hMailServer 6.3.4 and 6.3.5 allows a remote unauthenticated attacker to stop mail delivery by sending messages, when bounce processing or complaint processing is enabled or a mailing list is managed by the server (none is by default). The readers of incoming delivery status notifications (RFC 3464) and abuse feedback reports (RFC 5965) removed the blank lines at the start of the returned headers part two bytes at a time, copying the rest of the part each time, so their work grew with the square of the number of blank lines. A message shaped like such a report, whose headers part begins with a very large number of blank lines within the reader's 2 MB limit, keeps a delivery thread busy for over a minute while it is delivered, and a few such messages a minute keep every delivery thread busy.
Weakness: CWE-407
Which versions are affected by CVE-2026-107579?
How do I fix CVE-2026-107579?
No fix has been published for CVE-2026-107579 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-107579 being exploited?
There is no known exploitation of CVE-2026-107579 in the wild and no public exploit code.
Sources
Also known as GHSA-7658-76c6-34x2.